Some new energy automobile models comprise engine, electrical motor and transmission, so the space for entire vehicle layout is highly limited. A power on-off mechanism is necessarily required in order to reduce oil consumption, increase system efficiency, optimize control strategy and realize switching between different working modes. However, as traditional clutches comprise pressing plate, driven disk, diaphragm spring, release bearing, rocker, servomechanism etc., they have a large number of parts and components, a heavy weight as well as many invalidation points, and are hard to maintain.
It is disclosed in the prior art that electromagnetic dog clutches can replace traditional clutches. For example, a Chinese patent application of invention titled “Electromagnetic Toothed Clutch And Double-Motor Hybrid System” (application number: 201310741008.9) discloses an electromagnetic dog clutch, which is provided with a movable contrate gear and a fixed contrate gear (which may also be referred to as movable gear sleeve and fixed toothed sleeve). Under the attraction of the electromagnet the movable contrate gear engages with the fixed contrate gear and realizes inter-shaft transmission. The teeth of the movable contrate gear are rectangular, the tooth spaces of the fixed contrate gear are also rectangular, and the width of the tooth spaces are greater than that of the teeth, which facilitates the teeth entering the tooth spaces. The use of rectangular transmission teeth can improve the anti-interference ability of the system when the centering is not good, and can also promote the ability of torque transmission between contrate gears.
However, rectangular transmission teeth and tooth spaces have a defect that it is difficult to align and engage correctly, which will result in late clutching or invalidation of the clutch. Additionally, since the width of the tooth spaces are greater than that of the teeth, the engagement process has a defect that the teeth and the tooth spaces only in line contact and cannot completely realize surface contact.
As the movable contrate gear moves in the axis direction of the power output shaft and engages with the fixed contrate gear in the coaxial direction, after long time operation of the system, under the influence of wear or assembling relations, there will be a problem that the movable contrate gear cannot keep coaxial with the fixed contrate gear, which also results in late clutching or failure of the clutch.
In the above patent application, the clutch is also provided with an elastic resetting mechanism for resetting the movable contrate gear, to urge the movable contrate gear and the fixed contrate gear to separate. The elastic resetting mechanism comprises a positioning plate and a spring, the positioning plate is fixed to the end of the power output shaft, and the spring is located between the positioning plate and the movable contrate gear. When attracted by the electromagnet, the movable contrate gear moves towards the fixed contrate gear and compresses the spring; if the attraction of the electromagnet disappears, under the effect of the restoring force of the spring, the movable contrate gear moves away from the fixed contrate gear. As the attractive force of the electromagnet is generated instantly, the moving speed of the movable contrate gear is usually high, and thus it will drastically collide with the positioning plate and generate a remarkable system noise. Although a preloaded spring between them can provide a certain cushioning, the elastic modulus of the spring cannot be so high, otherwise the engagement between the movable contrate gear and the fixed contrate gear will be affected. Therefore, the cushioning effect of the spring is very weak, and cannot obviously reduce the system noise. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.